When an image is captured by an imaging device, a broad band of wavelengths is captured by the device. Depending on the finality of the image, not all the wavelengths are of use. In the case of imaging devices such as CMOS or CCD sensors of a digital camera, for example, only a small portion of the captured radiation is of use, this portion corresponding to the wavelengths of the visible domain. The infrared radiation, for example, that is undesired in the captured images then disrupts the image.
Specifically, infrared radiation also generates electrons by photoelectric effect. These electrons thus generated by the infrared radiation induce a signal which, by mixing with the signal corresponding to the visible radiation, will disrupt the measured signal and add an additional interference value to the useful signal. The quality of the images is thereby damaged.
In general, in order to filter the infrared radiation arriving on a photosite, the imaging devices such as CMOS or CCD sensors comprise an infrared filter placed above the photosite, that is to say between the incident radiations and the photosite. This infrared filtering prevents the infrared radiation from reaching the photosite while the visible radiation passes through the filter and can reach the photosite and generate electron-hole pairs then inducing a measurable signal.
The application of such infrared filters, usually produced in glass or in plastic, makes the production of an imaging device more complex, increases the production costs and increases the overall height since the height of the superposed infrared filter must be added to the height of the photosite.